Since posting this the other day I gave it some thought.
I thought that I could begin by putting the vehicle in the garage on stands similar to the anticpated height. Using a square to follow the contour of the inner quarter and lay this out (draw) on the garage floor. I can do this to follow the frame and any other points of reference ie center of axles,etc...

Once I have points of measurement I can easily figure out where the tire needs to be for clearance to the quarter panel. Then measure in the wheel and width of tires and lay this dimensions also on the floor.
Account for the disk brake roters and then I believe I have the appropriate rear end width.

I can mark up all new width dimensions for the frame in addtion to where I want the new Axle center line.

Once finished grab all measurements and put them on paper or in the cad drawing.

This should give me all of the x/y dimensions
I want to keep the inner wheel wheels looking as stock as possible so I believe I can just measure up from the frame to just under the wheel tubs so that the frame will remain under the inner fenders. (I realize that I will have to split and move inboard perhaps they may need to be widened as well.

With all the dimensions I can modify the extra frame to get it set for the body.

Does this sound like a realistic approach or can anyone provide advice that may be easier? I guess I'll need to do some heavy searching to see if there are builds that show how it was done.

Thanks,

-Ed

Perha

start measure back from the inner quarter reference line indicating the dimensions of the wheels